Process For Reducing Fouling In The Processing Of Liquid Hydrocarbons

ABSTRACT

The present invention relates to the use of a polyester which bears hydroxyl groups and is preparable by polycondensation of a polyol containing two primary OH groups and at least one secondary OH group with a dicarboxylic acid or anhydride thereof or ester thereof bearing a C 16 - to C 400 -alkyl radical or a C 16 - to C 400 -alkenyl radical as an antifoulant in the thermal treatment of liquid hydrocarbon media in the temperature range from 100 to 550 DEG C.

The present invention relates to a process for reducing fouling byliquid hydrocarbons during the processing thereof at relatively hightemperatures, for example in refinery operations.

In the course of processing, hydrocarbons such as crude oil andintermediates in mineral oil processing, for example, but alsopetrochemicals and petrochemical intermediates, are generally heated totemperatures between 100° C. and 550° C., frequently between 200° C. and550° C. In heating and heat exchange systems too, hydrocarbons used asheat carriers are exposed to such temperatures. In virtually all thesecases, hydrocarbons used form unwanted breakdown products or by-productsat elevated temperatures, which can separate out and accumulate at thehot surfaces of the heat transferers. The formation of these deposits isgenerally attributed to the presence of comparatively unstablecompounds, for example oxidized and/or oxidizable hydrocarbons andolefinically unsaturated compounds, but this is also blamed on highmolecular weight organic compounds and inorganic impurities. In specificcases, the extraneous substances which separate out and accumulate mayeven already be present in the raw material or precursor to beprocessed. In the specific case of mineral oil distillation, the crudeoils used for that purpose generally comprise constituents which lead todeposits, for example alkali metal and alkaline earth metal salts,compounds or complexes containing transition metals, for example ironsulfide or porphyrins, sulfur compounds, for example mercaptans,nitrogen compounds, for example pyrroles, compounds containing carbonylgroups or carboxyl groups, and polycyclic aromatics, for exampleasphaltenes and/or coke particles. In addition, the hydrocarbons usedfor processing virtually always contain small amounts of dissolvedoxygen.

The deposits which form in the course of processing of the hydrocarbonsat elevated temperatures and settle out on the surfaces in contact withthe liquid are referred to as fouling. They form particularly on the hotinsides of pipes, machines or heat exchangers.

These deposits in the processes mentioned gradually reduce the bore ofpipelines and vessels, which impairs both the process throughput andheat transfer. Often, the deposits even block filter screens, valves andtraps, and as a result cause plant shutdowns for cleaning andmaintenance. In all cases, these deposits are additionally unwantedby-products which reduce the yield of target product and hence lower theeconomic viability of the plant. In the case of heat exchange systems,the deposits form an insulating layer on the surfaces present, whichrestricts heat transfer. Consequently, the deposits necessitate frequentshutdowns of the plants for cleaning and in some cases even replacementthereof. Accordingly, these deposits are highly undesirable in industry.

The above-described deposits are usually higher molecular weightmaterials, the consistency of which may range from tar through rubberand “popcorn” to coke. The composition thereof may differ in nature andin many cases defies any detailed analysis. They often contain acombination of carbonaceous phases which are coke-like in nature,polymers and/or condensates which are formed from the hydrocarbons orimpurities present therein by various mechanisms. Further depositconstituents are frequently salts composed primarily of magnesiumchloride, calcium chloride and sodium chloride. The formation ofpolymers and/or condensates is attributed to catalysis by metalcompounds, for example compounds of copper or iron, which are present asimpurities in the hydrocarbons to be processed. Metal compounds of thiskind can, for example, accelerate the hydrocarbon oxidation rate bypromoting degenerative chain branching. The free radicals formed can inturn trigger oxidation and polymerization reactions, which leads to theformation of resins and sediments. Often, relatively inert carbonaceousdeposits are enclosed by more adhesive condensates or polymers.

Fouling deposits are equally encountered in the petrochemical field,where petrochemicals are either produced or purified. The deposits inthis environment are primarily polymeric in nature and have a severeeffect on the economic viability of the petrochemical operation. Thepetrochemical operations include, for example, the preparation ofethylene or propylene, or else the purification of chlorinatedhydrocarbons. Fouling is also observed in the processing of biogenic rawmaterials, for example in the processing of fatty acids and derivativesthereof, for example fatty acid esters.

To prevent the formation of deposits, oil-soluble, polar nitrogencompounds are used in many cases. These are predominantly reactionproducts of alkyl- or alkenylsuccinic acids or anhydrides thereof withpolyamines, which are optionally derivatized further.

For instance, U.S. Pat. No. 3,271,295 discloses reaction products ofalk(en)ylsuccinic anhydrides with polyamines for prevention of depositson metal surfaces in heat transferers in mineral oil refining.

WO-2011/014215 discloses the use of mono- and bisimides formed frompolyamines and C₁₀- to C₈₀₀-alkyl- or -alkenylsuccinic anhydrides forprevention of deposits in plants for mineral oil refining.

U.S. Pat. No. 5,342,505 discloses the use of reaction products formedfrom poly(alkenyl)succinimides with epoxyalkanols as antifoulants inliquid hydrocarbons during the processing thereof at elevatedtemperatures

U.S. Pat. No. 5,171,420 discloses reaction products formed fromalkenylsuccinic anhydrides, polyols, amines bearing hydroxyl groups,polyalkylenesuccinimides and polyoxyalkyleneamines for prevention ofdeposits in the course of heating of liquid hydrocarbons. In thepreferred embodiments, which are demonstrated by examples,polyfunctional reagents which lead to highly branched structures areused.

The reaction products of dicarboxylic acids with polyamines typicallyhave a relatively low molecular weight, since dicarboxylic acids, whencondensed with primary amines, react preferentially to give imides andform only minor proportions, if any, of diamides. Typically, thecondensation is restricted to the reaction of the primary amino groupsof the polyamine with one dicarboxylic acid each, such that the resultis typically molecular weights of not more than 3000 g/mol. Highermolecular weight compounds, which are desirable for the efficientreduction of fouling, are thus not obtainable in this way.

In addition, it is desirable from an economic point of view to useadditives having a minimum nitrogen content. As a result, any increasein the nitrogen content of the products obtained in the thermaltreatment of liquid hydrocarbons and any occurrence of by-products andresidues can be avoided. Both in the thermal treatment of liquidhydrocarbons themselves and in the subsequent further use of theproducts, by-products and residues obtained, an elevated content ofnitrogen compounds can lead to unwanted by-products and conversionproducts. For example, the combustion thereof forms nitrogen oxides.

There have been no descriptions to date of higher molecular weightoligomeric or even polymeric compounds and more particularly of highermolecular weight oligomeric or even polymeric nitrogen-free compoundsfor reduction of fouling by liquid hydrocarbons during the processingthereof at relatively high temperatures.

Higher molecular weight and additionally nitrogen-free condensates ofalkenylsuccinic acids are obtainable only by condensation with polyols,but these have been used to date only in entirely differentapplications.

For instance, EP-0809623 discloses oligomeric and polymeric bisesters ofalkyl- or alkenyldicarboxylic acid derivatives and polyalcohols, and theuse thereof as solubilizers, emulsifiers and/or wash-active substances.Preferred polyalcohols are glycerol and oligomeric glycerols.

WO-2008/059234 discloses oligo- and polyesters based onalk(en)ylsuccinic anhydrides and polyols having at least 3 hydroxylgroups and the use thereof as emulsifiers. These polymers areadditionally useful in the oilfield as foaming agents in foam drillingfluids, as kinetic gas hydrate inhibitors and as lubricants in aqueousdrilling fluids.

U.S. Pat. No. 4,216,114 discloses condensation products of C₉₋₁₈-alkyl-or -alkenylsuccinic anhydrides with water-soluble polyalkylene glycolsand polyols having at least 3 OH groups and the use thereof forsplitting water-in-oil emulsions.

U.S. Pat. No. 3,447,916 discloses condensation polymers ofalkenylsuccinic anhydrides, polyols and fatty acids for lowering thepour point of hydrocarbon oils. In these polymers, the hydroxyl groupsof the polyol are very substantially esterified.

DE-A-1920849 discloses condensation polymers of alkenylsuccinicanhydrides, polyols having at least 4 OH groups and fatty acids forlowering the pour point of hydrocarbon oils. Preferably, thestoichiometry of the reactants used for the condensation is selectedsuch that the number of moles of OH groups and carboxylic groups is thesame, meaning that there is substantially complete esterification.

WO-2011/076338 discloses low-temperature additives for middledistillates comprising polycondensates of a polyol containing twoprimary OH groups and at least one secondary OH group with adicarboxylic acid or anhydride thereof or ester thereof bearing a C₁₆-to C₄₀-alkyl radical or a C₁₆- to C₄₀-alkenyl radical.

The additives used according to the prior art for suppression or atleast for reduction of fouling often show deficits in the efficacythereof.

Consequently, there is a need for additives for more efficientsuppression or at least for reduction of the formation of sparinglysoluble deposits on the apparatus walls in the thermal treatment ofhydrocarbons, for example in processing and purifying plants, and alsoin heat exchange systems. These should preferably be nitrogen-free.Specifically, this need exists in the distillation of crude oils and inthe further processing of the mineral oil distillation fractions whichremain in distillation processes.

It has been found that, surprisingly, specific polycondensates ofdicarboxylic acids or dicarboxylic anhydrides bearing C₁₆-C₄₀₀-alkylradicals or C₁₆-C₄₀₀-alkenyl radicals and polyols having two primary andat least one secondary OH group achieve the stated objects. It has beenfound that higher molecular weight condensates having an essentiallylinear polymer backbone are particularly useful.

The invention accordingly provides for the use of a polyester whichbears hydroxyl groups and is preparable by polycondensation of a polyolcontaining two primary OH groups and at least one secondary OH groupwith a dicarboxylic acid or anhydride thereof or ester thereof whichbears a C₁₆- to C₄₀₀-alkyl radical or a C₁₆- to C₄₀₀-alkenyl radical asan antifoulant in the thermal treatment of liquid hydrocarbon mediawithin the temperature range from 100 to 550° C.

The present invention further provides a method for reducing fouling ina liquid hydrocarbon medium during the thermal treatment of the mediumat temperatures between 100 and 550° C., in which a polyester whichbears hydroxyl groups and is preparable by polycondensation of a polyolcontaining two primary OH groups and at least one secondary OH groupwith a dicarboxylic acid or anhydride thereof or ester thereof whichbears a C₁₆- to C₄₀₀-alkyl radical or a C₁₆- to C₄₀₀-alkenyl radical isadded to the liquid hydrocarbon before and/or during the thermaltreatment.

The invention further provides a method for increasing the service lifeof plants for thermal treatment of liquid hydrocarbon media within thetemperature range from 100 to 550° C., in which a polyester which bearshydroxyl groups and is preparable by polycondensation of a polyolcontaining two primary OH groups and at least one secondary OH groupwith a dicarboxylic acid or anhydride thereof or ester thereof whichbears a C₁₆- to C₄₀₀-alkyl radical or a C₁₆- to C₄₀₀-alkenyl radical isadded to a liquid hydrocarbon medium to be processed in the plant beforeand/or during the thermal treatment.

The polyester bearing hydroxyl groups is generally obtained by thepolycondensation of a dicarboxylic acid bearing a C₁₆- to C₄₀₀-alkylradical or -alkenyl radical, also referred to collectively hereinafteras C₁₆-C₄₀₀-alk(en)yl radical, with the primary hydroxyl groups of thepolyol. It is preferable that the secondary OH groups remain essentiallyunesterified. The preferred structure of the polyester bearing hydroxylgroups can thus be represented, for example, by formula (A):

in which

-   one of the R¹ to R⁴ radicals is a C₁₆-C₄₀₀-alkyl or -alkenyl radical    and-   the other R¹ to R⁴ radicals are each independently hydrogen or an    alkyl radical having 1 to 3 carbon atoms,-   R⁵ is a C—C bond or an alkylene radical having 1 to 6 carbon atoms,-   R¹⁶ is a hydrocarbyl group which bears at least one hydroxyl group    and has 3 to 10 carbon atoms,-   n is a number from 1 to 100,-   m is a number from 3 to 250,-   p is 0 or 1, and-   q is 0 or 1.

Preferred dicarboxylic acids which bear C₁₆-C₄₀₀-alkyl- and/or -alkenylradicals and are suitable for preparation of the polyesters A) bearinghydroxyl groups correspond to the formula (1)

in which

-   one of the R¹ to R⁴ radicals is a C₁₆-C₄₀₀-alkyl or -alkenyl radical    and-   the other R¹ to R⁴ radicals are each independently hydrogen or an    alkyl radical having 1 to 3 carbon atoms, and-   R⁵ is a C—C bond or an alkylene radical having 1 to 6 carbon atoms.

More preferably, one of the R¹ to R⁴ radicals is a C₁₆-C₄₀₀-alkyl- or-alkenyl radical, one is a methyl group and the rest are hydrogen. In aspecific embodiment, one of the R¹ to R⁴ radicals is a C₁₆-C₄₀₀-alkyl-or -alkenyl radical and the others are hydrogen. In a particularlypreferred embodiment, R⁵ is a C—C single bond. More particularly, one ofthe R¹ to R⁴ radicals is a C₁₆-C₄₀₀-alkyl- or -alkenyl radical, theother R¹ to R⁴ radicals are hydrogen and R⁵ is a C—C single bond.

The dicarboxylic acids or anhydrides thereof bearing alkyl- and/or-alkenyl radicals can be prepared by known processes. For example, theycan be prepared by heating ethylenically unsaturated dicarboxylic acidswith olefins or with chloroalkanes. Preference is given to the thermaladdition of olefins onto ethylenically unsaturated dicarboxylic acids oranhydrides thereof (“ene reaction”), which is typically conducted attemperatures between 100 and 250° C. The dicarboxylic acids anddicarboxylic anhydrides bearing alkenyl radicals which are formed can behydrogenated to dicarboxylic acids and dicarboxylic anhydrides bearingalkyl radicals. Dicarboxylic acids and anhydrides thereof preferred forthe reaction with olefins are maleic acid and more preferably maleicanhydride. Additionally suitable are itaconic acid, citraconic acid andanhydrides thereof, and the esters of the aforementioned acids,especially those with lower C₁-C₈-alcohols, for example methanol,ethanol, propanol and butanol.

In a first preferred embodiment, one of the R¹ to R⁴ radicals is alinear C₁₆-C₄₀-alkyl- or -alkenyl radical. For the preparation of suchdicarboxylic acids or anhydrides thereof bearing alk(en)yl radicals,preference is given to using olefins having 16 to 40 carbon atoms andespecially having 18 to 36 carbon atoms, for example having 19 to 32carbon atoms. In a particularly preferred embodiment, mixtures ofolefins having different chain lengths are used. Preference is given tousing mixtures of olefins having 18 to 36 carbon atoms, for examplemixtures of olefins in the C₂₀-C₂₂, C₂₀-C₂₄, C₂₄-C₂₈, C₂₆-C₂₈, C₃₀-C₃₆range. Olefin mixtures may also comprise minor proportions of shorter-and/or longer-chain olefins compared to the range specified, for examplehexene, heptene, octene, nonene, decene, undecene, dodecene, tetradeceneand/or olefins having more than 40 carbon atoms. Preferably, theproportion of the shorter- and longer-chain olefins in the olefinmixture is, however, not more than 10% by weight. More particularly, itis between 0.1 and 8% by weight, for example between 1 and 5% by weight.

Olefins particularly preferred for the preparation of the dicarboxylicacids or anhydrides thereof bearing C₁₆-C₄₀-alk(en)yl radicals have alinear or at least substantially linear alkyl chain. “Linear orsubstantially linear” is understood to mean that at least 50% by weight,preferably 70 to 99% by weight, especially 75 to 95% by weight, forexample 80 to 90% by weight, of the olefins have a linear componenthaving 16 to 40 carbon atoms and especially having 18 to 36 carbonatoms, for example having 19 to 32 carbon atoms. In a specificembodiment, α-olefins, wherein the C═C double bond is at the chain end,are used. Particularly useful olefins have been found to be technicalgrade alkene mixtures. These contain preferably at least 50% by weight,more preferably 60 to 99% by weight and especially 70 to 95% by weight,for example 75 to 90% by weight, of terminal double bonds (α-olefins).In addition, they may contain up to 50% by weight, preferably 1 to 40%by weight and especially 5 to 30% by weight, for example 10 to 25% byweight, of olefins having an internal double bond, for example havingvinylidene double bonds having the structural element R¹⁷—CH═C(CH₃)₂where R¹⁷ is an alkyl radical having 12 to 36 carbon atoms andespecially having 14 to 32 carbon atoms, for example having 15 to 28carbon atoms. In addition, minor amounts of secondary components presentfor technical reasons, for example paraffins, may be present, butpreferably not more than 5% by weight. Particular preference is given toolefin mixtures containing at least 75% by weight of linear α-olefinshaving a carbon chain length in the range from C₂₀ to C₂₄.

In a further preferred embodiment, one of the R¹ to R⁴ radicals is aC₄₁-C₄₀₀-alkyl- or -alkenyl radical and especially a C₅₀- to C₃₀₀-alkylor -alkenyl radical, for example a C₅₅- to C₂₀₀-alkyl- or -alkenylradical. Preferably, this alk(en)yl radical is branched. Additionallypreferably, these C₄₁-C₄₀₀-alk(en)yl radicals derive from polyolefinspreparable by polymerization of monoolefins having 3 to 6 and especiallyhaving 3, 4 or 5 carbon atoms. Particularly preferred monoolefins asbase structures for the polyolefins are propylene and isobutene, whichgive rise to poly(propylene) and poly(isobutene) as polyolefins.Preferred polyolefins have an alkylvinylidene content of at least 50 mol%, particularly of at least 70 mol % and especially at least 80 mol %,for example at least 85 mol %. “Alkylvinylidene content” is understoodto mean the content in the polyolefins of structural units which resultfrom compounds of the formula (3):

in which R⁶ or R⁷ is methyl, ethyl or propyl and especially methyl andthe other group is an oligomer of the C₃-C₆-olefin. The alkylvinylidenecontent can be determined, for example, by means of ¹H NMR spectroscopy.The number of carbon atoms in the polyolefin is between 41 and 400. In apreferred embodiment of the invention, the number of carbon atoms isbetween 50 and 3000 and especially between 55 and 200. The parentpolyolefins of the C₄₁-C₄₀₀-alkyl- or -alkenyl radical are obtainable,for example, by ionic polymerization and are available as commercialproducts (e.g. Glissopal®, polyisobutenes from BASF with differentalkylvinylidene content and molecular weight). Also suitable inaccordance with the invention are mixtures of various polyolefins, inwhich case these may differ, for example, in terms of the parentmonomers, the molecular weights and/or the alkylvinylidene content.

Preferred polyesters bearing hydroxyl groups are preparable by reactionof alkyl- or alkenylsuccinic acids and/or anhydrides thereof bearing aC₁₆-C₄₀₀-alkyl- or -alkenyl radical with polyols bearing two primary andat least one secondary hydroxyl group.

Preferred polyols may be monomeric, oligomeric or polymeric in terms ofstructure. Polymers and oligomers are referred to collectively aspolymers. R¹⁶ in formula A) is preferably a radical of the formula (2)

—(CH₂)_(r)—(CH(OH))_(t)—(CH₂)_(s)—  (2)

in whicht is a number from 1 to 6,r and s are each independently a number from 1 to 9 andt+r+s is a number from 3 to 10.

In monomeric polyols, n in formula A) is 1. Preferred monomeric polyolshave three to 10 and especially four to six carbon atoms. Theyadditionally have at least one and preferably 1 to 6, for example 2 to4, secondary OH groups, but not more than one OH group per carbon atom.Suitable monomeric polyols are, for example, glycerol,1,2,4-butanetriol, 1,2,6-trihydroxyhexane, and also reducedcarbohydrates and mixtures thereof. Reduced carbohydrates are understoodhere to mean polyols which derive from carbohydrates and bear twoprimary and two or more secondary OH groups. Particularly preferredreduced carbohydrates have 4 to 6 carbon atoms. Examples of reducedcarbohydrates are erythritol, threitol, adonitol, arabitol, xylitol,dulcitol, mannitol and sorbitol. A particularly preferred monomericpolyol is glycerol.

In polymeric polyols, n in formula A) is a number from 2 to 100,preferably a number from 2 to 50, more preferably a number from 3 to 25and especially a number from 4 to 20. Preferred polymeric polyols havesix to 150, especially eight to 100 and particularly nine to 50 carbonatoms. They bear at least one, preferably two to 50 and especially threeto 15 secondary OH groups, but not more than one OH group per carbonatom. Polymeric polyols suitable in accordance with the invention arepreparable, for example, by polycondensation of polyols having twoprimary and at least one secondary OH group. A preferred polymericpolyol is poly(glycerol). “Poly(glycerol)” is especially understood tomean structures derivable by polycondensation from glycerol. Thecondensation level of poly(glycerols) preferred in accordance with theinvention is between 2 and 50, more preferably between 3 and 25 andespecially between 4 and 20, for example between 5 and 15.

The preparation of poly(glycerol) is known in the prior art. It can beprepared, for example, via addition of 2,3-epoxy-1-propanol (glycide)onto glycerol. In addition, poly(glycerol) can be prepared bypolycondensation, as known per se, of glycerol. The reaction temperaturein the polycondensation is generally between 150 and 300° C., preferablybetween 200 and 250° C. The polycondensation of glycerol is normallyconducted at atmospheric pressure. Catalyzing acids include, forexample, HCl, H₂SO₄, organic sulfonic acids or H₃PO₄; catalyzing basesinclude, for example, NaOH or KOH. The catalysts are added to thereaction mixture preferably in amounts of 0.01 to 10% by weight, morepreferably 0.1 to 5% by weight, based on the weight of the reactionmixture. The polycondensation of glycerol can be conducted withoutsolvent, or else in the presence of solvent. If the polycondensation iseffected in the presence of solvent, the proportion thereof in thereaction mixture is preferably 0.1 to 70% by weight, for example 10 to60% by weight. Preferred organic solvents here are the solvents alsoused and preferred for the condensation of the dicarboxylic acid,anhydride thereof or ester thereof bearing alk(en)yl radicals with thepolyol. The polycondensation of glycerol generally takes 3 to 10 hours.This process is also applicable mutatis mutandis to the polycondensationof other polyols.

The dicarboxylic acid, anhydride thereof or ester thereof bearingalk(en)yl radicals are converted to the polyester bearing hydroxylgroups preferably in a molar ratio of 1:2 to 2:1, more preferably in amolar ratio of 1:1.5 to 1.5:1 and especially in a molar ratio of 1:1.2to 1.2:1, for example in a equimolar ratio. More preferably, theconversion is effected with an excess of polyol. In this context, molarexcesses of 1 to 10 mol % and especially 1.5 to 5 mol % based on theamount of dicarboxylic acid used have been found to be particularlyuseful.

The polycondensation of the dicarboxylic acid, anhydride thereof orester thereof bearing alkyl radicals with the polyol is effectedpreferably by heating C₁₆-C₄₀₀-alkyl- or -alkenyl-substituteddicarboxylic acid or the anhydride or ester thereof together with thepolyol to temperatures above 100° C. and preferably to temperaturesbetween 120 and 320° C., for example to temperatures between 150 and290° C. For adjustment of the molecular weight, which is important forthe efficacy of the polyester bearing hydroxyl groups, it is typicallynecessary to remove the water of reaction or the alcohol of reaction,which can be effected, for example, by distillative removal. Azeotropicremoval by means of suitable organic solvents is also suitable for thispurpose. Preferred solvents for the polycondensation of the dicarboxylicacid, anhydride thereof or ester thereof bearing alk(en)yl radicals withthe polyol are relatively high-boiling, low-viscosity solvents.Particularly preferred solvents are aliphatic and aromatic hydrocarbonsand mixtures thereof. Aliphatic hydrocarbons preferred as solvents have9 to 20 carbon atoms and especially 10 to 16 carbon atoms. They may belinear, branched and/or cyclic. They are preferably saturated or atleast substantially saturated. Aromatic hydrocarbons preferred assolvents have 7 to 20 carbon atoms and especially 8 to 16, for example 9to 13, carbon atoms. Preferred aromatic hydrocarbons are mono-, di-,tri- and polycyclic aromatics. In a preferred embodiment, these bear oneor more, for example two, three, four, five or more, substituents. Inthe case of a plurality of substituents, these may be the same ordifferent. Preferred substituents are alkyl radicals having 1 to 20 andespecially having 1 to 5 carbon atoms, for example methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl,tert-pentyl and neopentyl radical. Examples of suitable aromatics arealkylbenzenes and alkylnaphthalenes. For example, aliphatic and/oraromatic hydrocarbons or hydrocarbon mixtures, e.g. petroleum fractions,kerosene, decane, pentadecane, toluene, xylene, ethylbenzene orcommercial solvent mixtures such as Solvent Naphtha, Shellsol® AB,Solvesso® 150, Solvesso® 200, Exxsol® products, ISOPAR® products andShellsol® D products, are particularly suitable. As well as the solventsbased on mineral oils, solvents based on renewable raw materials andsynthetic hydrocarbons obtainable, for example, from the Fischer-Tropschprocess, are suitable as solvents. Also suitable are mixtures of thesolvents mentioned. If the polycondensation is effected in the presenceof solvent, the proportion thereof in the reaction mixture is preferably1 to 75% by weight and especially 10 to 70% by weight, for example 20 to60% by weight. The condensation is preferably conducted without solvent.

For acceleration of the polycondensation, it has often been found to beuseful to conduct the polycondensation in the presence of homogeneouscatalysts, heterogeneous catalysts or mixtures thereof. Preferredcatalysts here are acidic inorganic, organometallic or organic catalystsand mixtures of two or more of these catalysts.

Acidic inorganic catalysts in the context of the present invention are,for example, sulfuric acid, phosphoric acid, phosphonic acid,hypophosphorous acid, aluminum sulfate hydrate, alum, acidic silica geland acidic aluminum hydroxide. Additionally usable as acidic inorganiccatalysts are, for example, aluminum compounds of the formula Al(OR¹⁵)₃and titanates of the formula Ti(OR¹⁵)₄, where the R¹⁵ radicals may eachbe the same or different and are each independently selected fromC₁-C₁₀-alkyl radicals, for example methyl, ethyl, n-propyl, isopropyl,n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl,sec-pentyl, neopentyl, 1,2-dimethylpropyl, isoamyl, n-hexyl, sec-hexyl,n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl or n-decyl, C₃-C₁₂-cycloalkylradicals, for example cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl,cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl andcyclododecyl; preference is given to cyclopentyl, cyclohexyl andcycloheptyl. Preferably, the R¹⁵ radicals in Al(OR¹⁵)₃ and Ti(OR¹⁵)₄ areeach the same and are selected from isopropyl, butyl and 2-ethylhexyl.

Preferred acidic organometallic catalysts are, for example, selectedfrom dialkyltin oxides (R¹⁵)₂SnO where R¹⁵ is as defined above. Aparticularly preferred representative of acidic organometallic catalystsis di-n-butyltin oxide, commercially available as “oxo-tin” or as theFascat® brand.

Preferred acidic organic catalysts are acidic organic compounds having,for example, phosphate groups, sulfo groups, sulfate groups orphosphonic acid groups. Particularly preferred sulfonic acids contain atleast one sulfo group and at least one saturated or unsaturated, linear,branched and/or cyclic hydrocarbyl radical having 1 to 40 carbon atomsand preferably having 3 to 24 carbon atoms. Especially preferred arearomatic sulfonic acids and specifically alkylaromatic monosulfonicacids having one or more C₁-C₂₈-alkyl radicals and especially thosehaving C₃-C₂₂-alkyl radicals. Suitable examples are methanesulfonicacid, butanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid,xylenesulfonic acid, 2-mesitylenesulfonic acid, 4-ethylbenzenesulfonicacid, isopropylbenzene-sulfonic acid, 4-butylbenzenesulfonic acid,4-octylbenzenesulfonic acid, dodecyl-benzenesulfonic acid,didodecylbenzenesulfonic acid and naphthalenesulfonic acid. It is alsopossible to use acidic ion exchangers as acidic organic catalysts, forexample poly(styrene) resins which bear sulfo groups and have beencrosslinked with about 2 mol % of divinylbenzene.

For the performance of the process according to the invention,particular preference is given to boric acid, phosphoric acid,polyphosphoric acid and polystyrenesulfonic acids. Especially preferredare titanates of the formula Ti(OR¹⁵)₄ and specifically titaniumtetrabutoxide and titanium tetraisopropoxide.

If it is desirable to use acidic inorganic, organometallic or organiccatalysts, according to the invention, 0.01 to 10% by weight, preferably0.02 to 2% by weight, of catalyst is used. In a specific embodiment, thecondensation is effected without addition of catalysts.

In a preferred embodiment, for adjustment of the molecular weight, minoramounts of the dicarboxylic acids, anhydrides thereof or esters thereofbearing alk(en)yl radicals are replaced in the reaction mixture by C₁-to C₁₈-monocarboxylic acids, preferably C₂- to C₁₆-monocarboxylic acidsand especially C₃- to C₁₄-monocarboxylic acids, for example C₄- toC₁₂-monocarboxylic acids. At the same time, however, not more than 20mol % and preferably 0.1 to 10 mol %, for example 0.5 to 5 mol %, of thedicarboxylic acids, anhydrides thereof or esters thereof bearingalk(en)yl radicals is replaced by one or more monocarboxylic acids. Inaddition, minor amounts, for example up to 10 mol % and especially 0.01to 5 mol % of the alk(en)ylsuccinic acids or anhydrides thereof may alsobe replaced by further dicarboxylic acids, for example succinic acid,glutaric acid, maleic acid and/or fumaric acid. More preferably, thepolyesters bearing hydroxyl groups are prepared in the absence ofmonocarboxylic acids.

In a further preferred embodiment, for adjustment of the molecularweight, minor amounts of the polyol are replaced in the reaction mixtureby C₁- to C₃₀-monoalcohols, preferably C₂- to C₂₄-monoalcohols andespecially C₃- to C₁₈-monoalcohols, for example C₄- to C₁₂-monoalcohols.At the same time, preferably not more than 20 mol % and more preferably0.1 to 10 mol %, for example 0.5 to 5 mol %, of the polyol is replacedby one or more monoalcohols. More preferably, the polyesters bearinghydroxyl groups are prepared in the absence of monoalcohols. Inaddition, the polyol bearing two primary and at least one secondaryhydroxyl groups may also be replaced by one or more diols in minoramounts of up to 10 mol %, for example 0.01 to 5 mol %. Preference isgiven here to diols, for example ethylene glycol, propylene glycoland/or neopentyl glycol. More preferably, the polyesters bearinghydroxyl groups are prepared in the absence of diols.

In a further preferred embodiment, to increase the molecular weight,minor amounts of the polyol bearing two primary and at least onesecondary OH group are replaced in the reaction mixture by polyolshaving three or more primary OH groups, for example having four, five,six or more primary OH groups. At the same time, preferably not morethan 10 mol % and more preferably 0.1 to 8 mol %, for example 0.5 to 4mol %, of the polyol bearing two primary and at least one secondary OHgroup is replaced by a polyol having three or more primary OH groups.Suitable polyols having three or more primary OH groups are, forexample, trimethylolethane, trimethylolpropane and pentaerythritol.

The mean condensation level of the polyesters bearing hydroxyl groupsused in accordance with the invention is preferably between 4 and 200,more preferably between 5 and 150, especially between 7 and 100 andparticularly between 10 and 70, for example between 15 and 50, repeatdicarboxylic acid and polyol units. The condensation level is understoodhere to mean the sum of m+p+q as per formula (A). The weight-averagemolecular weight Mw of the polyesters bearing hydroxyl groups,determined by means of GPC in THF against poly(ethylene glycol)standards, is preferably between 2000 g/mol and 600 000 g/mol. In thecase of polyesters which derive from dicarboxylic acids bearingC₁₆-C₄₀-alk(en)yl radicals, it is more preferably between 2000 and 100000 g/mol and especially between 3000 and 50 000 g/mol, for examplebetween 4000 and 20 000 g/mol. In the case of polyesters which derivefrom dicarboxylic acids bearing C₄₁-C₄₀₀-alk(en)yl radicals, it is morepreferably between 3000 and 500 000 g/mol, particularly between 5000 and200 000 g/mol and especially between 8000 and 150 000 g/mol, for examplebetween 10 000 and 100 000 g/mol.

Preferably, the acid number of the polyesters bearing hydroxyl groups isless than 40 mg KOH/g and more preferably less than 30 mg KOH/g, forexample less than 20 mg KOH/g. The acid number can be determined, forexample, by titration of the polymer with alcoholictetra-n-butylammonium hydroxide solution in xylene/isopropanol.Additionally preferably, the hydroxyl number of the polyesters isbetween 40 and 500 mg KOH/g, more preferably between 50 and 300 mg KOH/gand especially between 60 and 250 mg KOH/g. The hydroxyl number can,after reaction of the free OH groups with isocyanate, be ascertained bymeans of ¹H NMR spectroscopy, by quantitative determination of theurethane formed.

Preferably, the polyesters bearing hydroxyl groups used in accordancewith the invention are nitrogen-free. “Nitrogen-free” is understood inaccordance with the invention to mean that the nitrogen content thereofis below 1000 ppm by weight and more preferably below 100 ppm by weightand especially below 10% by weight, for example below 1 ppm by weight.The nitrogen content can be determined, for example, according toKjeldahl.

The term “liquid hydrocarbon medium”, according to the invention,represents various different mineral oil hydrocarbons andpetrochemicals. For example, mineral oil hydrocarbon feedstocksincluding crude oils and fractions obtainable therefrom, for examplenaphtha, gasifier fuel, kerosene, diesel, jet fuel, heating oil, gasoil, vacuum residues inter alia are covered by this definition. Examplesof petrochemicals are olefinic or naphthenic process streams, aromatichydrocarbons and derivatives thereof, ethylene dichloride and ethyleneglycol. Likewise covered by the term “liquid hydrocarbon media” arehydrocarbons used as heat carriers, for example fused and/or substitutedaromatics. Additionally covered by this definition are biogenic rawmaterials and products obtainable from biogenic raw materials byprocessing, for example animal and vegetable oils and fats andderivatives thereof, for example fatty acid alkyl esters. The liquidhydrocarbon media may also comprise constituents not consisting ofhydrocarbons, for example salts, minerals and organometallic compounds.

The polyesters used in accordance with the invention are added to theliquid hydrocarbon media preferably in amounts of 0.5 to 5000 ppm byweight, more preferably of 1.0 to 1000 ppm by weight, for example of 2to 500 ppm by weight. The polyesters may be dispersed or dissolved inthe liquid hydrocarbon medium. They are preferably dissolved.

For easier handling, the polyesters used in accordance with theinvention are preferably dissolved or dispersed in a polar or nonpolarorganic solvent and added to the liquid hydrocarbon medium as aconcentrate. Preferred solvents here are the solvents and solventmixtures already mentioned as solvents for the condensation reactionbetween dicarboxylic acid and polyol. Particular preference is given toaromatic solvents. Preferably, the proportion of the polyester in theconcentrate is 5 to 95% by weight, more preferably 10 to 80% by weightand especially 20 to 70% by weight, for example 25 to 60% by weight.

The polyester is preferably added to the liquid hydrocarbon medium priorto the thermal treatment thereof. The addition can be undertakenbatchwise, for example into the storage vessel of the liquid hydrocarbonmedium, or continuously into the feed line to the heat treatment plant.The addition is preferably effected at a site where the temperature ofthe liquid hydrocarbon medium is at least 10° C. and especially at least20° C., for example at least 50° C., below the maximum heat treatmenttemperature. Especially in the case of hydrocarbon media of relativelyhigh viscosity, it has often been found to be useful to promote themixing of the polyester into the liquid hydrocarbon medium by means ofstatic or dynamic mixing apparatus.

Particular advantages are shown by the inventive use of polyestersbearing hydroxyl groups and by the method that utilizes them in theprocessing or treatment of liquid hydrocarbon media above 100° C.,especially between 150 and 500° C. and particularly between 200° C. and480° C., for example between 250° C. and 450° C.

The polyesters used in accordance with the invention can be usedtogether with one or more further additives. Preferred further additivesare pour point depressants and demulsifiers, the latter preferably basedon alkoxylated alkylphenol-aldehyde resins.

The inventive use of polyesters bearing hydroxyl groups in the thermaltreatment of liquid hydrocarbon media leads to a reduction in foulingsuperior to the prior art additives and often also to the substantialand in some cases even complete suppression thereof. As a result, theenergy requirement in the processing of liquid hydrocarbon is loweredand the throughput of the plant and the yield of target product areincreased.

The method of the invention is generally suitable for reducing and ofteneven for suppressing fouling in the processing of liquid hydrocarbonmedia at relatively high temperatures. This lowers the energyrequirement of the process and increases the throughput of the plant andthe yield of target product. The reduction in fouling reduces thefrequency of maintenance shutdowns for removal of deposits and henceincreases the plant availability.

For instance, the methods of the invention have been used successfullyfor reduction of fouling in crude oil distillation, in the processing ofintermediates in mineral oil processing and in the processing ofpetrochemicals, and also of petrochemical intermediates, for example ofgases, oils and reforming feedstocks, chlorinated hydrocarbons andliquid products from olefin plants, for example of bottoms phases fromdeethanization. The methods have likewise been used successfully forreduction and often for suppression of fouling by hydrocarbons used asheating media on the ‘hot side’ of heat exchange systems.

The suitability of the additives used in accordance with the inventionfor suppression or at least for reduction of fouling by liquidhydrocarbons in the course of thermal treatment thereof can be measured,for example, with commercially available HLPS (Hot Liquid ProcessSimulation) systems. In these systems, the oil to be treated thermallyis pumped continuously through a capillary with a heating elementpresent therein. As a result of fouling, deposits gradually form on theheating element, which impair heat transfer and lead to a pressure dropover the capillary. The extent of fouling can be assessed, for example,via the drop in the temperature at the outlet of the capillary. Asignificant drop in the temperature during the experiment indicates theoccurrence of fouling. Measurements of this kind are generally regardedas a measure for assessment of the tendency of an oil to fouling in heatexchangers.

EXAMPLES

The α-olefins used were commercially available mixtures of 1-alkenes orpoly(isobutenes) having the compositions specified. The acid numberswere determined by titration of an aliquot of the reaction mixture withalcoholic tetra-n-butylammonium hydroxide solution inxylene/isopropanol. The hydroxyl numbers were determined, after reactingthe free OH groups of the polymers with isocyanate, by means of ¹H NMRspectroscopy, by quantitative determination of the urethane formed. Thevalues reported are based on the solvent-free polymers.

The molecular weights were determined by means of lipophilic gelpermeation chromatography in THF against poly(ethylene glycol) standardsand detection by means of an RI detector.

Polyesters used:

-   P1) Copolymer of equimolar proportions of C₂₀₋₂₄-alkenylsuccinic    anhydride (prepared by thermal condensation of maleic anhydride with    technical-grade C₂₀₋₂₄-olefin containing, as main constituents, 43%    C₂₀-, 35% C₂₂- and 17% C₂₄-olefin, with 90% α-olefins and 7.5%    linear internal olefins) and glycerol. The reactants, in the form of    a 50% solution in Shellsol® AB (aromatic solvent mixture having a    boiling range of about 185-215° C.), were heated to 150° C. while    stirring until the acid number remained constant. The water which    formed was distilled off. The acid number of the polymer thus    prepared was 7.8 mg KOH/g, the hydroxyl number was 98 mg KOH/g and    the weight-average molecular weight was 6100 g/mol.-   P2) Copolymer prepared in analogy to example P1) from equimolar    proportions of C_(20/24)-alkenylsuccinic anhydride (prepared by    thermal condensation of maleic anhydride with technical-grade    C_(20/24)-olefin containing, as main constituents, 43% C₂₀-, 35%    C₂₂- and 17% C₂₄-olefin, with 90% α-olefins and 7.5% linear internal    olefins) and poly(glycerol) having a mean condensation level of 3.    The acid number of the polymer was 6.5 mg KOH/g, the hydroxyl number    was 195 mg KOH/g and the weight-average molecular weight was 8700    g/mol.-   P3) Copolymer prepared in analogy to example P1) from equimolar    proportions of C_(26/28)-alkenylsuccinic anhydride (prepared by    thermal condensation of maleic anhydride with technical-grade    C₂₆₋₂₈-olefin containing, as main constituents, 57% C₂₆-, 39% C₂₈-    and 2.5% C₃₀₊-olefin, with 85% α-olefins, 4% linear internal olefins    and 9% branched olefins) and glycerol. The acid number of the    polymer was 10.4 mg KOH/g, the hydroxyl number was 68 mg KOH/g and    the weight-average molecular weight was 9100 g/mol.-   P4) Copolymer of C_(20/24)-alkenylsuccinic anhydride as per example    P1, 0.7 molar equivalent of glycerol and 0.3 molar equivalent of    behenic acid. The acid number of the polymer was 15 mg KOH/g, the    hydroxyl number was 32 mg KOH/g and the weight-average molecular    weight was 1800 g/mol.-   P5) Copolymer of equimolar proportions of C₂₀₋₂₄-alkenylsuccinic    anhydride and ethylene glycol in analogy to example P1. The acid    number of the polymer thus prepared was 8.2 mg KOH/g, the hydroxyl    number was 2 mg KOH/g and the weight-average molecular weight was    5700 g/mol (comparative example).-   P6) C₂₀₋₂₄-Alkenylsuccinic anhydride as per example P1, reacted with    2 molar equivalents of triethylenetetramine. The reactants, in the    form of a 50% solution in Shellsol AB, were heated to 150° C. while    stirring until the acid number remained constant. The water which    formed was distilled off. The acid number of the polymer thus    prepared was 10.2 mg KOH/g and the weight-average molecular weight    was 1000 g/mol (comparative example).-   P7) Copolymer prepared in analogy to example P1) from equimolar    proportions of poly(isobutenyl)succinic anhydride (prepared by    thermal condensation of maleic anhydride with poly(isobutene) having    a mean molecular weight Mn of 1000 g/mol and an alkylvinylidene    content of 87 mol %) and glycerol. The acid number of the polymer    was 8.6 mg KOH/g, the hydroxyl number was 47 mg KOH/g and the    weight-average molecular weight was 14 000 g/mol.-   P8) Copolymer prepared in analogy to example P1) from equimolar    proportions of poly(isobutenyl)succinic anhydride (prepared by    thermal condensation of maleic anhydride with poly(isobutene) having    a mean molecular weight Mn of 2300 g/mol and an alkylvinylidene    content of 81 mol %) and poly(glycerol) having a mean condensation    level of 5. The acid number of the polymer was 7.8 mg KOH/g, the    hydroxyl number was 110 mg KOH/g and the weight-average molecular    weight was 21 000 g/mol.

The efficacy of the additives in terms of their ability to prevent orreduce fouling by mineral oils on hot surfaces was tested with the aidof a modified Hot Liquid Process Simulation (HLPS) system from Alcor. Inthe HLPS system, the oil to be examined was pumped continuously from astirred and heated reservoir vessel through an electrically heatedheating element mounted in a stainless steel capillary (=hot capillary),before being returned to the reservoir vessel. During the experiment,the maximum oil temperature attained after switching on the heating (thesurface temperature of the heating element was about 400° C.) wasfirstly registered at the output of the stainless steel capillary (T1).Secondly, the oil temperature was registered at the same point after anexperimental duration of 5 hours (T2). Since the deposits formed on theheating element as a result of fouling have low thermal conductivity,the maximum temperature initially attained correlates indirectly (lowinitial temperature T1 implies immediate onset of fouling), and thedifference in the temperatures T2 and T1 directly, with the extent offouling.

For each experiment, about 500 ml of the oil sample to be examined wereintroduced into the reservoir vessel and heated to about 150° C. forbetter pumpability. The oil was then pumped at a volume flow rate of 3ml/min through the stainless steel capillary which has been providedwith a clean heating element with a bare surface. The heating elementwas then heated to a temperature of about 400° C. for test oil 1, about375° C. for test oil 2 or about 390° C. for test oil 3, and the maximumoil temperature which was then established at the capillary outlet wasnoted (T1). After a run time of 5 hours, the oil temperature that wasthen present at the end of the stainless steel capillary (T2) was notedand the experiment was ended. A high maximum temperature T1 and a low ΔT(ΔT=T2−T1) indicate low coverage of the surface of the heating elementwith insulating deposits and hence effective suppression of fouling.

The following test oils were used for the assessment of thefouling-reducing effect of the additives:

Test oil 1 2 3 Origin Brazil Malaysia Thailand API gravity @ 15° C. 25.747.2 11.4 [°API] Viscosity [mPas] 61 5 160 (25° C.) (25° C.) (50° C.)Density [g/cm³] 0.900 0.792 0.990 (20° C.) (20° C.) (16° C.) Pour point[° C.] −27 +18 +33 Asphaltene content 7.9 3.2 10.3 [% by wt.]

The viscosity was determined to ASTM D-445, and the density to DIN ENISO 12185. The pour point was determined to ASTM D-97. The asphaltenecontent was determined to IP 143.

Experimental Results in Test Oil 1

Dosage T1 T1 Fouling Measure- Addi- rate (t = 0) (t = 5 h) ΔT reductionment tive [ppm] [° C.] [° C.] [° C.] [%]  1 none — 278 256 22 0  2 P1 5281 266 15 32  3 P2 5 282 268 14 36  4 P3 5 281 266 15 32  5 P4 5 280262 18 18  6 (comp.) P5 5 279 257 22 0  7 (comp.) P6 5 280 261 19 14  8P1 10 283 269 14 36  9 P2 10 285 274 11 50 10 P3 10 283 271 12 45 11 P410 281 265 16 27 12 (comp.) P5 10 279 259 20 9 13 (comp.) P6 10 282 26418 18 14 P1 15 285 274 11 50 15 P2 15 286 278 8 64 16 P3 15 285 275 1055 17 P4 15 284 270 14 36 18 (comp.) P5 15 280 261 19 14 19 (comp.) P615 283 266 17 23

Experimental Results in Test Oil 2

Dosage T1 T1 Fouling Measure- Addi- rate (t = 0) (t = 5 h) ΔT reductionment tive [ppm] [° C.] [° C.] [° C.] [%] 20 none 0 257 230 27 0 21 P1 10261 238 23 15 22 P2 10 262 239 23 15 23 P3 10 261 238 23 15 24 P4 10 260236 24 11 25 (comp.) P5 10 258 231 27 0 26 (comp.) P6 10 260 235 25 7 27P1 25 263 244 19 30 28 P2 25 263 243 20 26 29 P3 25 262 243 19 30 30 P425 261 240 21 22 31 (comp.) P5 25 258 234 24 11 32(comp.) P6 25 262 23923 15 33 P1 50 264 253 11 59 34 P2 50 265 256 9 67 35 P3 50 263 253 1063 36 P4 50 261 247 14 48 37 (comp.) P5 50 260 241 19 30 38 (comp.) P650 261 245 16 41

Experimental Results in Test Oil 3

Dosage T1 T1 Fouling Measure- Addi- rate (t = 0) (t = 5 h) ΔT reductionment tive [ppm] [° C.] [° C.] [° C.] [%] 39 none 0 266 244 22 0 40 P1 10270 254 16 27 41 P2 10 271 256 15 32 42 (comp.) P5 10 265 244 21 5 43(comp.) P6 10 268 250 18 18 44 P7 10 271 257 14 36 45 P8 10 273 261 1245 46 P1 20 272 259 13 41 47 P2 20 272 260 12 45 48 (comp.) P5 20 265245 20 9 49 (comp.) P6 20 270 253 17 23 50 P7 20 273 262 11 50 51 P8 20274 264 10 55 52 P1 40 273 262 11 50 53 P2 40 274 264 10 55 54 (comp.)P5 40 266 246 20 9 55 (comp.) P6 40 271 258 13 41 56 P7 40 275 266 9 5957 P8 40 275 268 7 68

The decreases in temperature after an experimental duration of 5 hoursobserved in the experiments using the method of the invention are muchsmaller than in comparative experiments using other methods oradditives. Moreover, higher maximum temperatures are generally observedat first. Both indicate lower deposits on the heating element and hencemore efficient suppression of fouling in the case of inventive use ofthe additives or of the method that utilizes them. Accordingly, themethod of the invention entails less frequent maintenance of the plantfor removal of the deposits and hence longer service lives of the plant.Since the target oil temperature is often preset in industrial plants,the method of the invention additionally leads to saving of energy.

1. The use of a polyester which bears hydroxyl groups and is preparableby polycondensation of a polyol containing two primary OH groups and atleast one secondary OH group with a dicarboxylic acid or anhydridethereof or ester thereof which bears a C₁₆- to C₄₀₀-alkyl radical or aC₁₆- to C₄₀₀-alkenyl radical as an antifoulant in the thermal treatmentof liquid hydrocarbon media within the temperature range from 100 to550° C.
 2. The use as claimed in claim 1, wherein the OH number of thepolyester is at least 40 mg KOH/g.
 3. The use as claimed in claim 1and/or 2, wherein the dicarboxylic acid or anhydride thereof or esterthereof bears a C₁₆- to C₄₀-alkyl radical or a C₁₆- to C₄₀-alkenylradical.
 4. The use as claimed in claim 3, wherein the dicarboxylic acidis a C₁₆- to C₄₀-alkyl- or C₁₆- to C₄₀-alk(en)ylsuccinic acid oranhydride thereof.
 5. The use as claimed in one or more of claims 1 to4, wherein the alkyl or alkenyl radical of the dicarboxylic acid oranhydride thereof or ester thereof contains 18 to 36 carbon atoms. 6.The use as claimed in one or more of claims 3 to 5, wherein the alkyl oralkenyl radical derives from an α-olefin.
 7. The use as claimed in claim1 and/or 2, wherein the dicarboxylic acid or anhydride thereof or esterthereof bears a C₄₁- to C₄₀₀-alkyl radical or a C₄₁- to C₄₀₀-alkenylradical.
 8. The use as claimed in claim 7, wherein the alkyl or alkenylradical of the dicarboxylic acid is branched.
 9. The use as claimed inclaim 7 and/or 8, wherein the alkyl or alkenyl radical derives from apolyolefin.
 10. The use as claimed in claim 9, wherein the polyolefinderives from an olefin having 3 to 6 carbon atoms.
 11. The use asclaimed in claim 10, wherein the polyolefin is poly(isobutene).
 12. Theuse as claimed in one or more of claims 1 to 11, wherein the polyol isof monomeric structure, and comprises three to 10 carbon atoms and 1 to6 secondary OH groups, but not more than one OH group per carbon atom.13. The use as claimed in one or more of claims 1 to 11, wherein thepolyol is of polymeric structure and comprises six to 150 carbon atomsand two to 50 secondary OH groups, but not more than one OH group percarbon atom.
 14. The use as claimed in one or more of claims 1 to 11,wherein the polyol is selected from glycerol and oligomers thereofhaving 2 to 10 monomer units.
 15. The use as claimed in one or more ofclaims 1 to 14, wherein the polyester corresponds to the structuralformula (A)

in which one of the R¹ to R⁴ radicals is a C₁₆-C₄₀₀-alkyl or -alkenylradical and the other R¹ to R⁴ radicals are each independently hydrogenor an alkyl radical having 1 to 3 carbon atoms, R⁵ is a C—C single bondor an alkylene radical having 1 to 6 carbon atoms, R¹⁶ is a hydrocarbylgroup which bears at least one hydroxyl group and has 3 to 10 carbonatoms, n is a number from 1 to 100, m is a number from 3 to 250, p is 0or 1, and q is 0 or
 1. 16. The use as claimed in claim 15, wherein oneof the R¹ to R⁴ radicals is a linear C₁₆-C₄₀-alkyl or -alkenyl radical.17. The use as claimed in claim 15, wherein one of the R¹ to R⁴ radicalsis a C₄₁-C₄₀₀-alkyl or -alkenyl radical.
 18. The use as claimed in claim9, wherein R¹⁶ is a radical of the formula (2)—(CH₂)_(r)—(CH(OH))_(t)—(CH₂)_(s)—  (2) in which t is a number from 1 to6, r, s are each independently a number from 1 to 9 and t+r+s is anumber from 3 to
 10. 19. The use as claimed in one or more of claims 1to 18, wherein the polyester is nitrogen-free.
 20. The use as claimed inone or more of claims 1 to 19, wherein the molecular weight of thepolyester is between 2000 g/mol and 100 000 g/mol.
 21. The use asclaimed in one or more of claims 1 to 20, wherein the liquid hydrocarbonmedium is crude oil or a fraction obtainable from crude oil.
 22. The useas claimed in one or more of, claims 1 to 21, wherein the liquidhydrocarbon medium is a petrochemical or a hydrocarbon used as a heatcarrier.
 23. The use as claimed in one or more of claims 1 to 22,wherein the liquid hydrocarbon medium is of biogenic origin.
 24. The useas claimed in one or more of claims 1 to 23, wherein the use is effectedat temperatures between 200 and 550° C.
 25. A method for reducingfouling in a liquid hydrocarbon medium during the heat treatment of themedium at temperatures between 100 and 550° C., in which the polyesterbearing hydroxyl groups as defined in one or more of claims 1 to 20 isadded to the liquid hydrocarbon before and/or during the thermaltreatment.
 26. A method for increasing the service life of plants forthermal treatment of hydrocarbons, in which the polyester bearinghydroxyl groups as defined in one or more of claims 1 to 20 is added tothe hydrocarbon media to be processed before and/or during the thermaltreatment.
 27. The method as claimed in claim 25 or 26, which proceedsat temperatures of 200 to 550° C.